1. Field of the Invention
The invention relates to a position detecting system and a detecting method and, more particularly, to a position detecting system and a position detecting method for detecting the position of a capsule body-insertable apparatus which is introduced in a subject by using a magnetic field.
2. Description of the Related Art
In recent years, a capsule body-insertable apparatus having an imaging device (hereinbelow, called a capsule endoscope) is developed. The capsule endoscope is introduced into a subject, for example, via the oral route, captures an image of the inside of the subject, and transmits the obtained image (hereinbelow, called an in-vivo image) to an apparatus disposed on the outside of the subject by radio. The operator can diagnose a symptom or the like of the subject by visually recognizing the in-vivo image received by the outside apparatus.
Such a capsule endoscope usually cannot move in a subject by itself and is moved in a subject by peristaltic movement of digestive organs of the subject. Consequently, there is a case such that, for example, as compared with an endoscope with which an observation region can be selected by the operator freely to a certain degree such as a fiber scope, the observation capability of the capsule endoscope is lower.
An example of techniques for solving such a drawback is the technique disclosed in Japanese Laid-open Patent Publication No. 2005-245963. According to the conventional art, by applying a magnetic field (hereinbelow, called a guidance magnetic field) from the outside of a subject to a capsule endoscope having magnetic field generating means such as a permanent magnet, the posture and movement of the capsule endoscope can be positively controlled from the outside of the subject.
In order to control the posture and movement of the capsule endoscope in the subject by the magnetic field applied from the outside of the subject like in the conventional art, however, the position, direction, and the like of the capsule endoscope in the subject have to be known accurately. In the following, detection of the position and direction (posture) of the capsule endoscope will be simply called position detection.
In the conventional art, by providing a resonance circuit having a coil (L) and a capacitor (C) (hereinbelow, called an LC resonance circuit) in the capsule endoscope and detecting an induced magnetic field generated by a magnetic field applied from the outside (hereinbelow, called a drive magnetic field) by the LC resonance circuit, the position and direction of the capsule endoscope are detected. In the following, the method of deriving information of the position, direction, and the like from the induced magnetic field generated by applying the drive magnetic field to the LC resonance circuit from the outside will be called a passive method.
The conventional art also describes a configuration that a resonance frequency signal is supplied to the LC resonance circuit mounted on the capsule endoscope and an excitation magnetic field generated by the signal is detected, thereby detecting the position and direction of the capsule endoscope. In the following, a method of deriving information such as position and direction from an excitation magnetic field generated by applying a resonance frequency signal to the LC resonance circuit will be called an active method.